Nitric oxide (NO) is a potent, critical, multifaceted bioregulatory agent. This project is aimed at a) finding ways to target NO to specific sites in the body for important research and/or drug development applications, and b) characterizing the possible role of NO as a determinant of cancer risk. a) Several promising developments have occurred during this reporting period in our continuing effort to solve important clinical problems by exploiting our accumulating knowledge of the chemistry of the NO-releasing diazeniumdiolates (compounds containing the [N(O)NO]- functional group, formerly called 'NONOates'). Polymers containing the diazeniumdiolate function not only inhibited proliferation of vascular smooth muscle cells in vitro but also markedly suppressed adhesion of platelets to normally thrombogenic vascular grafts placed in the baboon circulatory system, suggesting their possible utility for improving vascular graft technology as well as reducing the risk of restenosis after angioplasty. Drugs of the diazeniumdiolate series have also been found to induce penile erections in cats, revealing a potential role in treating impotence; and to inhibit the attachment of tumor cells to isolated venules in vitro, suggesting possible utility for preventing metastases. b) In our studies of NO as a potentially genotoxic agent, E. coli that was transformed with DNA treated in vitro with an NO-releasing diazeniumdiolate at a concentration of only 1 microM showed markedly increased mutation frequency, but DNA damage could not be detected in cultured human cells treated with the same compound at a 4000-fold higher concentration. We conclude that NO has inherent DNA-damaging potential but that cellular defenses have evolved to protect the mammalian genome from the possible deleterious effects of this critical bioregulatory agent. We regard this as a particularly important project, and will place particular emphasis during the coming year on designing drugs and devices capable of targeting NO release to select tissues for therapeutic benefit. At the same time, we will continue to characterize NO~s potential activity as a pro- or anticarcinogen.